This application is based on applications No. 11-066404 and 11-106773 filed in Japan, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a contents copying system, copying method, computer-readable recording medium and disc drive copying contents recorded on one recording medium onto a different recording medium.
2. Description of the Background Art
DVD-ROMs (Digital Versatile Disc Read-Only Memory) and DVD-RAMs (Digital Versatile Disc Random Access Memory) are portable optical discs which can store 4.7 gigabytes of data on a single side, despite having a diameter of only 120 mm. Such discs are soon expected to come into widespread use. Since both have a logical format ideally suited for recording computer data, movies and music, it is likely that disc drives capable of accessing both DVD-ROMs and DVD-RAMs will be provided as standard equipment in most personal computers in the near future.
When the DVD-ROM format used is DVD-Audio, the copyright owner requires that copying of data stored on a disc be strictly limited using a standard DVD copyright protection method and CCI (Copy Control Information). The following is a brief outline of such a method. First, a content is recorded on a recording medium such as a DVD-Audio disc after being encrypted using a cipher key (generally known as the title key) determined by the content owner. One title key is generally provided for each group of contents, or title, and one or more titles may be recorded on a single disc. The title key is encrypted using a cipher key unique to that particular DVD-Audio disc (generally known as the disc key) and recorded in a sector header area on the DVD-Audio disc. The disc key itself is encrypted using another cipher key (generally known as the master key) determined by the manufacturers of contents decoders, and recorded in a lead-in area of the DVD-Audio disc. The sector header area and the lead-in area cannot be accessed by ordinary users, making it extremely difficult to obtain title keys recorded on the DVD-Audio disc.
The following is an explanation of how the contents are used by devices.
The above described DVD copyright protection method does not restrict the transmission of encrypted contents between devices, but rather completely prohibits the output of unencrypted contents between devices. Furthermore, the method imposes strict limitations on the transfer of title keys between devices. This applies both to when two devices such as a DVD-Audio drive and a contents decoder are connected and contents reproduced, and to when two devices such as a DVD-Audio drive and a DVD-RAM drive are connected and contents are copied from DVD-Audio onto DVD-RAM. Basically, a title key can only be transmitted if two devices have successfully performed mutual authentication, thereby confirming whether they are legitimate devices compliant with the DVD copyright protection standard. Here, a title key is not transmitted between the devices after being encrypted by the disc key, but is transmitted after being encrypted by another cipher key (the session key) which was shared by the devices when mutual authentication was performed. FIG. 1A shows a contents reproduction system formed from a connected DVD-Audio disc drive and contents decoder. The disc drive in the drawing has a disc access unit 101 for reading contents from a DVD-Audio disc, and a bus authentication unit 102 for performing mutual authentication with a connected device-via a bus, and the decoder has a bus authentication unit 103 for performing mutual authentication with a connected device via a bus, a descrambler 104 for descrambling encrypted contents using a title key, and an audio decoder 105 for reproducing contents that have been descrambled. In the drawing, the title key is transferred after the bus authentication units 102 and 103 have authenticated each other, thereby enabling the reproduction of contents to be prohibited if a bogus device has been connected.
Finally, the copying of contents between two connected disc drives is explained. Copying performed by a standard computer system, or so-called file copying, is performed by reading contents recorded on an original recording medium and recording it unchanged onto a target recording medium. Legitimate contents copying, however, cannot take place simply by reading encrypted contents recorded on an original recording medium and recording it onto a copy target. Additional processing needs to be performed before this procedure can truly be referred to as contents copying. In this processing, a title key recorded on the original recording medium is read and decrypted using the disc and master keys, then information unique to the target recording medium is read from the target recording medium and used to reencrypt the title key before it is recorded on the target recording medium. The processing for decrypting and then reencrypting a title key is necessary in contents copying because the decoder in the contents reproduction system of FIG. 1A requires the connected disc drive to transfer a legitimate title key.
Contents copying is performed as in the above description. Under the DVD-Video standard, such contents copying has been completely prohibited at the request of the video contents providers. In the case of audio contents, however, making copies for personal use, such as from CD to MD (Mini Disc(trademark)), is widely accepted, and so there was a need to accommodate such copying under the DVD-Audio standard. CCI (Copy Control Information) is specified by the DVD-Audio standard to enable contents copying to be performed under certain conditions. CCI corresponding to each content is set in a DVD-Audio disc. CCI may be set at any one of four.levels for each content. These levels are xe2x80x98copy freexe2x80x99 allowing copies to be made freely, xe2x80x98copy oncexe2x80x99 allowing a first-generation copy to be made, xe2x80x98no more copiesxe2x80x99 prohibiting additional copies being made, and xe2x80x98never copyxe2x80x99 prohibiting copying altogether. When CCI for a content is xe2x80x98copy oncexe2x80x99, the number of copies may be set at between one and ten.
A DVD-Audio disc drive is equipped with a copy authorization control unit that determines whether copies are authorized by referring to CCI. This means that the copy authorization control unit holds copy management information, consisting of ID information for the contents which have already been recorded on the DVD-RAM, and a number of copies showing the number of times that each content has been recorded. When a content is recorded on DVD-RAM, the copy authorization control unit is responsible for increasing the number of copies, and prohibiting copying after the number of copies reaches the number shown in the CCI. If the CCI shows that contents copying is authorized by the copy authorization control unit, the title key is transmitted between the devices via mutual authentication, as explained above, and recorded on DVD-RAM. FIG. 1B shows a contents copying system formed from two connected disc drives: a playback drive (player) for reading contents from a DVD-Audio disc, and a recorder drive (recorder) for recording contents on DVD-RAM. The player and recorder in the contents copying system shown in the drawing respectively include disc access units 111 and 112 accessing DVD-Audio and DVD-RAM, bus authentication units 113 and 114 performing mutual authentication via a bus, and copy authorization control units 115 and 116 determining what restrictions have been placed on copying the contents of the DVD-Audio disc. Only if the copy authorization control units 115 and 116 determine that copying is authorized, and bus authentication units 113 and 114 confirm the authenticity of the opposing device in each case, is encrypted contents copied from DVD-Audio onto DVD-RAM, along with the encrypted title key.
However, an individual user must acquire both the player for reading contents from DVD-Audio and the recorder for recording contents onto DVD-RAM if they wish to copy audio contents, so that the need to purchase two disc drives, which may place an unnecessary economic burden on users. In particular, even though many DVD-RAM recorders are also capable of playback, neither the DVD-Audio nor copyright protection standards disclose any techniques for copying contents using only one such drive.
A first object of the invention is to provide a content copying system and disc drive capable of content copying when the playback and record functions are included in the same disc drive.
A second object is to provide a content copying system and disc drive capable of copying contents from a first recording medium to a second recording medium, even when transmission of a cipher key between devices is strictly limited in accordance with the DVD copyright protection standard.
Suppose the disc drive is connected to a host computer having an internal hard disk. Here, the host computer is provided with a bus authentication unit 114, and a copy authorization control unit 115, so that it should be possible to perform the above-mentioned content copying between the disc drive and the host computer. This may be performed by having the disc drive read a cipher key and a content stored on DVD-Audio, and storing the content and cipher key into the hard disk inside the host computer, reading them from the hard disk to be stored onto DVD-RAM. However, performing content copying by making a further copy onto DVD-RAM of a content and cipher key copied onto the hard disk is equivalent to making a second generation copy.
Under the DVD-Audio standard, contents often have a CCI set at xe2x80x98copy oncexe2x80x99 in order to prevent content proliferation. As a result, content copying performed via the hard disk of the host computer is equivalent to a second generation copy and may be prohibited by the copy authorization unit 116.
In order to prevent such copying being equivalent to second generation copying, as well as to achieve the first and second objects, a content copying system with the following construction is provided. This content copying system includes a host computer and a disc drive and makes first generation copies, but prohibits second generation copies onwards. The disc drive includes a first unit and a second unit. When a first recording medium has been loaded, the first unit reads an encrypted content and a cipher key from the first recording medium, transmits the encrypted content to the host computer and stores the cipher key inside the disc drive. When a rewritable second recording medium is loaded after the first recording medium has been loaded, the second unit obtains the encrypted content from the host computer and the cipher key stored inside the disc drive, and records the obtained encrypted content and cipher key onto the second recording medium. In this content copying system, a single disc drive combining both playback and record functions is connected to a host computer having a hard disk, enabling legitimate content copying to be performed from a first recording medium onto a second recording medium. Since the user does not need to acquire two disc drives, content copying can be realized at low cost. Here, an encrypted content is copied by transmitting it from the first recording medium to the host computer and then from the host computer to the second recording medium, but the cipher key is not transmitted to the host computer. Since the encrypted content is not transmitted to the host computer together with the cipher key, this does not correspond to content copying as disclosed by the DVD copyright protection standard. This is because the transmission of a content from the host computer to the second recording medium does not correspond to a second generation copy, so that even if the CCI prohibits second generation copies of the content, it can still be copied from the first recording medium onto the second recording medium.
The content copying system may also have the following construction. Here, the first recording medium holds a piece of identification (ID) information with a linked piece of copy limiting information, the piece of ID information identifying the encrypted content recorded on the first recording medium, and the piece of copy limiting information indicating how many first generation copies are authorized for the encrypted content. The disc drive includes a secure storage medium and a setting unit. When the encrypted content is transmitted to the host computer, the setting unit sets the piece of ID information, the linked piece of copy limiting information, and an initial value for a copy number showing how many first generation copies of the content have been made, in the secure storage medium. The second unit includes a recording unit and an updating unit. When a rewritable second recording medium is loaded after the first recording medium has been loaded, the recording unit records the encrypted content and the cipher key onto the second recording medium. The updating unit updates the copy number stored in the secure storage medium each time recording is performed by the recording unit. In the above construction, the copy number is not incremented when the encrypted content is transmitted to the host computer and stored in the hard disk, but only when the encrypted content is recorded onto the second recording medium, so the content can be used by the second recording medium. This means that the user can take the second recording medium one which the content has been recorded, and playback the content in a variety of devices, including component sound systems, and portable sound systems.
The content copying system may also have the following construction. Here, the disc drive includes, a comparing unit and a duplicate ID information determining unit. When one of the second recording medium and another second recording medium is loaded after recording of the encrypted content has been completed by the recording unit, the comparing unit compares the copy number and the piece of copy limiting information for the encrypted content. The duplicate ID information determining unit determines whether the media ID information for the loaded second recording medium has already been written into the secure storage medium, linked to the piece of ID information for the encrypted content. The recording unit records the encrypted content from the host computer onto the loaded second recording medium when the copy number is less than the piece of copy limiting information for the encrypted content, or the duplicate ID information determining unit determines that the media ID information for the loaded second recording medium has already been set in the secure storage medium. In this construction, if the content recorded on the second recording medium was mistakenly deleted by the user, a special copy of the content from the host computer onto the second recording medium may be permitted even if the number of copies exceeds the copy limiting number, thereby allowing the deleted content to be reconstructed. This is permitted if the media ID for the second recording medium is the same as that for a second recording medium onto which the content has previously been copied.
The content copying system may also have the following construction. Here, the cipher key has been encrypted using a disc key unique to the first recording medium, and recorded on the first recording medium. The first unit includes a cipher key setting unit for fetching the disc key unique to the first recording medium and writing the fetched disc key into the secure storage medium inside the disc drive, so as to link the disc key to the cipher key. The second unit includes a cipher key descrambler for decrypting the encrypted cipher key stored in the secure storage medium once the second recording medium has been loaded, using the disc key unique to the first recording medium, a cipher key scrambler that reads the media ID information for the second recording medium, and encrypts the decrypted cipher key using the media ID information for the second recording medium; and a cipher key recording unit that records the cipher key encrypted by the cipher key scrambler onto the second recording medium. In this construction, the cipher key is encrypted by unique media ID information for the second recording medium when recorded onto the second recording medium, thereby enabling content copying to be performed while following the stipulations made in the DVD copyright protection method.
The content copying system may also include a host computer and a disc drive, that makes first generation copies, but prohibits second generation copies onwards, by recording an encrypted content and a cipher key recorded on a first recording medium onto a second recording medium. The disc drive includes the following. A reading unit reads an encrypted content and a cipher key from a first recording medium when the first recording medium is loaded. A temporary storage key holding unit holds a temporary storage key differing from the cipher key. A first scrambler decrypts, using the cipher key, the encrypted content read from the first recording medium, then encrypts the decrypted content using the temporary storage key held in the temporary storage key holding unit and transmits the encrypted content to the host computer. When a rewritable second recording medium is loaded after the first recording medium has been loaded, a second scrambler decrypts, using the temporary storage key, the encrypted content obtained from the host computer, and then encrypts the decrypted content using the cipher key. A recording unit records the content encrypted by the second scrambler onto the second recording medium. In this construction, the content is encrypted using a temporary storage key when stored temporarily in the hard disk inside the host computer. This temporary storage key differs from the cipher key used to encrypt the content when it is stored on the first recording medium. This means that if the content stored on the hard disk inside the host computer is illegally analyzed, the risk of the cipher key being exposed is reduced.